Thank for your answers, it works! But I'd prefer to use the relative way because I'm displaying the first div in different height depending of the position of the device. So I edited the example (first div height is auto)
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Darf ZonJan 31 '13 at 21:27

then honestly its going to be either really hacky, or you're looking at a javascript solution.
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PlantTheIdeaJan 31 '13 at 21:32